Modulation of high-frequency currents



R. A. HEISING.

MODULANON OF HIGH FREQUENCY CUHRENTS. APPLICATION FILED AUG.25,1915.

W/Tnesses: /n we n/o r: 67%. M Raymond A He/5mg.

Patented May 25, 1920.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISINGyOF EAST ORANGE, NEW JERSEY, ASSIGNOR, BY MESNEASSIGN- KENTB, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A. CORPORATIONOF NEW YORK.

MODULATION OF HIGH-FREQUENCY CUBRENTS.

Patented May 25, 1920.

Application filed August 25, 1915. Serial No. 47,332.

To all whom it'may concern:

Be it known that I, RAYMOND A. Hmsixo, a citizen of the United States,residing at East Orange, in the county of and State of New Jersey, haveinvented certain newand useful Improvements in Modulawith the signals tobe transmitted.

In view of the extreme sensitivity of a generator electro-motive forceto variations in the current of the fieldwindings, it has been. sugested that the signaling device he put in t e field circuit, thecurrent of which will be modulated in accordance with speech. However,althoughthe power used in the field windings is small compared to theoutput of the generator. it is still true that the wet required for thefield is excessively arge for a telephone transmitter. Furthermore, theimpedance of the field coil is large compared to that of the usual modulator or: signaling device. such as the microphone trii'iismitter,-\vhereas-cithas been found desirable that they should be of about thesame magnitude. or that the impedance 1 of the modulator should begreater than that of the field coil. This isnecessar-y in order toobtain etlicient or complete modulation. In other words. itis necessarythat the modulator shall becapable of absorbing as much power as thefield coils. Moreover, when a 'microphone is placed directly in thecircuit of the field coil, the time constant is not ordinarily therebyreduced to a value which will 'prevent undue distortion of the,modulating currents because of the low-resistance of the microphone.

According to this invention the above noted defects are overcome orgreatly reduced by placing the field or energizing winding in circuitwith a space discharge device and pro erly proportioning the impedanceof sait device with respect to that of the energizing winding. Formaximum etliciency it has been found desirable to make the impedance ofthe space discharge device of the same orderot magnitude as that of thefield winding. as explained above. However it may sometimes be desirableto provide a lower space discharge impedance in case the time constantis for any reason to be increased and 111 case maximum efliciency is notthe primary consideration. If

desired, the impedance of the space discharge device may be increasedtoa value greater than that of the field coil for the purpose ofreducing the time constant of the field circuit. A spacedischarge devicesuitable for this purpose is one, such as that described below. having aheated cathode and having the property of amplifying voltage variationsimpressed upon its input circuit.

Referring to the figure, an elevated antenna or other suitable radiatingsystem, is in circuit with the high frequency generator 2 which isconnected to the antenna on the one side and to the earth on the other.Sustained oscillations will thus be radiated from the elevated antenna.The field wind ing '3 of the generator 2 is connected in series to theoutput circuit of the thermionic space discharge device 4. This deviceashere shown is substantially the same as that which is now employed asan amplifier of, telephonic currents- It comprises an evacuatedvessel inwhich there is a heated cathode "5. an impedance varying element 6. in

the form of a grid. and a plate anode 7. Any known form of dischargedevice having an element by means of which the impedance of thedischarge path may be varied, may be employed, The grid circuit of thedischarge device includes the secondary of the transformer 9, theprimary of which contains the battery 10 and microphone transmitter 11.or its equivalent.

The impedance of that part of the discharge device which is in circuitwith the energizing winding of the generator is made of the proper valueto give the desired re sults in accordance with the principles set"therefore modulated in accordance with the signals impressed on themicrophone. This modulated field current will impress correspondingmodulations. upon the high frequency power radiated from the antenna.

Although the primary object of this invention is to provide a method andmeans for modulating the high frequency power used in wirelesstelegraphy or telephony in accordance with the signals to betransmitted, certain features of the invention. as defined in theappended claims. are capable of quite general application. as will beevidentto those skilled in the art. The invert 'Ifli-lOIL. may. lieemployedcin sygiteng ma king use of a transmission hne in place ofantennae. It is obvious also that the receiving relay current may beused for any desired purpose, such as the distant control of switchingor other mechanism. The microphone 11 may be replaced by othercontrolling means such ascircuit controlling means used in telegraphsystems.

By characterizing the frequency of the oscillations produced by thegenerator as high, it is meant that this frequency is high as comparedwith essential voice or signaling frequencies. It is obvious that theinvention is applicable toany form of generator in which there is anenergizing wind ing having a source of current for supplying initialenergy for the generation of the oscillations.

at is claimed is: 1. The method of controlling the amplitude anddistortion of the output waves of an alternating current generatorhaving a 'wind-ingsupplied with current partat-Jeast of the energy ofwhich current is employed in the production of said output waves. whichmethod comprises generating control currents, causing a part of theenergy of said supplied current to be absorbed without inductive action.and simultaneously variably controlling the energy thus absorbed inaccordance with said control currents. A

2. The method of controlling fluctuating currents produced by agenerator having a winding supplied with current. part at least of theenergy from which is employed in the production of said fluctuatingcurrents, which method comprises causing a part of the energy of saidsupply current to be absorbed in a space discharge. and simultaneouslyvariably controlling the energy thus absorbed.

3. The method of controlling fluctuating electrostatically variablycontrolling during such absorption the portion of energy thus absorbed.

:l. The method of controlling high frequency oscillations produced by agenerator having a winding supplied with current, part at least of theenergy of which current is.cmployed in the production of said highfrequency oscillations, which method comprises causing a part of theenergy of said current to be absorbed without inductive action, andsimultaneously electrically controlling in accordance with speechcurrents the energy thus absorbed. j. The method of controlling currentsproddee d by a generator having a winding supplied with current, part atleast of the energy of which current is employed in the production ofthe generated currents, which method comprises causing part of theenergy of said supply current to be absorbed in a space discharge andsimultaneously controlling the energy thus absorbed.

(3. The method of controlling current produced by a generator having awinding supplied with current, part at least of the energy of whichcurrent is employed in the production of the generated currents, whichmethod comprises causing a part of the energy of said supply current tobe absorbed in a space discharge and simultaneously controlling theenergy thus absorbed by varying the impedance of the space .dischargepath.

7. The method of controlling currents produced by a generator having awinding supplied with current. part at least of the 'rnergywt'.whichcurrentds employedin the production of the generated currents,which method comprises causing a part of the energy of said supplycurrent to be absorbed in a space discharge and simultaneouslycontrolling the energy thus absorbed by varying the electric field inthe vicinity of the space discharge.

8. In a high frequency signaling system. a generator of high frequencyoscillations having a field winding, a source of low power oscillations.a large variable impedance of at least the same order of magnitude asthat of said field winding controlled by said source, and means wherebythe variations in said impedance control the current in the fieldwinding of said generator.

9. In a high frequency signaling system, a generator of high frequencyoscillations having a field winding, a telephone transmitter forproducing low power signaling oscillations, a variable impedance ofapproximately the same value as the impedance of said field winding.said variable impedance being adapted to be varied by said low poweroscillations. and means for connecting said variable impedance to saidfield winding, thereby controlling the current in said field winding inaccordance with said variable impedance. I

10. In a high frequency signaling'system;

a generator of high frequency oscillations havin a field windin asourceiof'low fre 5 n I a I quency oscillations, a variable impedancehaving a value at least of the same order of magnitude as theimpedanceofsaid-field' winding. said variable impedance being adapted tobe varied by saii'l low frequency' source, and means forassociating saidvariable nnpeda-nce witli'f-said field wind ng,

thereby controlling thecurrent in said field winding in accordance Iwith r said" variable impedance.

11. In a high frequency signaling system, a generator of high frequencyoscillations having a field-winding, a source oflow frequencyoscillations, a variable impedance having aval-ue of approximately thesame order of magnitude as the impedance of a generator of highfrequency oscillations ha'v1ng a field winding, a thermionic amplifierconnected to said field Winding, and

v a'signaling device associated with said amplifier to modulate theimpedance of said field winding in accordance with signals to betransmitted, said field winding having an impedance greater than that ofsaid signaling device.

In witness whereof, I hereunto subscribe my name this 19th day ofAugust, A. D. 1915.

RAYMOND A. HEISING.

